Cheapest priced copy (Commander 2011): $0.35 at Card Kingdom, near mint, their price list as of .
Prison Term 
Enchantment — Aura · Uncommon · Planechase · #6
Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.
Whenever a creature an opponent controls enters, you may attach this Aura to that creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
4 printings · $0.35 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2011 | 27 | Uncommon | $0.35 | — |
| Planechase | 6 | Uncommon | $0.35 | — |
| The List | SHM-18 | Uncommon | $0.35 | — |
| Shadowmoor | 18 | Uncommon | $0.39 | $2.49 |
2 rulings from Wizards of the Coast
- 1 May 2008The last ability works only if Prison Term is already on the battlefield. You may move it from the creature it's currently enchanting onto the new creature.
- 8 June 2016Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.